I have noticed that in most Monotheistic religions, the one god tends to be perfect, reflecting the best that you can be. The family tree is consequently quite small.

However, in most Polytheistic religions the pantheon tends to have specific things assigned to each member. These things are not only spheres of influence, but personality traits as well. This makes the gods of Polytheistic religions more human. Whatever type of person you are or situation you find yourself in, there is a Greek deity to illustrate the relevant issues.

This also leaves the gods open to jokes, as they are not supposed to be perfect, and so they may not do the right thing, and be lightly chided for it, with more safety than defying a single God who, if proven imperfect, tends to be nasty. A very general example of imperfection is that the Greek gods were very prone to having many love affairs, despite prior marriage(s)! This is played for laughs often, and also gives an opportunity to add in reasons why many of the heroes were "special"

In the transfer process from Greek to Roman mythology not only the names of the gods were changed. Overall the behavioral changes were slight, but the huge shift from Ares to Mars should not go unnoticed. In Greek mythology Ares is a loathsome coward, shown as a bully who cannot tolerate pain or any other such thing. He is cruel and bloodthirsty, unlike Mars who is a stalwart upright warrior. Mars is very prideful, as is Ares, although Mars has reason to be, as in combat he does not run away at the slightest wound.

The way a people depict their gods is an important thing. The Greek depiction of War, which is shown through Ares, is decidedly negative, while the Roman image of War, which Mars acts as the avatar for, is a role model for people to follow. This shows that the Romans saw war more gloriously than the Greeks.